Idle prob- In and out of gear

[mugsy]

When the car is in park the engine will idle around 1300 rpm. As soon as I drop it into gear it goes down to 600-700. Now the carb is a YF from a '69 250 (or at least that's what I told the part person at O'Reilly's). I went with that carb when I upgraded to a DS-II.

I don't know if the problem is torque converter related or carb related. But the idle in gear is pretty rough (it was worse) and it just doesn't idle smoothly. ut out of gear she is almost as smooth as silk.

 

[MPGmustang]

check fluids, check vacum hose's for leaks, check timing (what's it at), check vacum (what's it at),

try setting timing at 10*

then move the gas/air idle screw to idle the fastest
check vacum, then move the timing to get ~20 (best/ideal) (from manifold only)
then move the gas/air idle screw to idle the fastest again (check)
then check vacum, if not at 20 then adjust to 20 again

go back and forth till you get the fastest idle with the 20 vacum

then change idle to get desired idle range (you want to idle in gear at 650+)

take her to the road and find a hill, if you floor it up the hill and she pings,
back off 2* timing, move gas/air for 20 again, set idle when in gear.

it's time consuming to fine tune any car, but it's worth it when it just works!
Richard

 

[mugsy]

Sorry about that... OK, I've checked for leaks and can't find any. Checked the carb and base with carb cleaner. I've also taken the hoses off and capped the nipples, so I've verified that the hoses are good. Current timing is 12*. At the rebuild I went with 9.1 CR to avoid pinging/spark knock. The cam is a Comp or Crane cam with advertised 268 duration both intake and exhaust. The vacuum reads like 15 to 17 and it jumps a bunch. The cam was recently re-timed to 4* advanced on the adjustable timing set I got from CI. Prior to that at 2* retard and 4* retard the engine ran very hot (200F with a 160F T/stat) and the vac was 13 and jumped around a ton. I had set the needle to highest vacuum and it had the really bad idle. So I just turned it a 1/4 more out and got it to this point. I've had the needle almost all the way out and the vac never gets above 15-17.

 

[JackFish]

I would've started with the cam timing straight up.
That way you have one less variable with which to deal.
Your vacuum readings look OK for that cam. You can expect lower vacuum with a higher performance cam.
You probably find that the mix screw doesn't do much to alter the rpms.
How well is the idle speed screw functioning? I ended up drilling a small hole in the throttle plate, and it allowed me to close the throttle plate further down into the transfer circuit. It really improved the low end tune-ability and drive-ability.

 

[mugsy]

Well I've tried three different YF and this is the best running one so far. What I did was drill out the idle jet with a #52 I think and that actually helped a bunch. On one of the other YF's I tried drilling a small hole in the throttle plate and that had zero effect. I tried increasing the hole size but again, no change to the idle quality. So (with that carb at least) I figured it wasn't an air issue.

Is there any way to test the torque converter? The carb runs great off idle, so the main circuit is good. she has plenty of pep and good acceleration for a mild build 200 straight 6.

 

[MPGmustang]

Your vacuum readings look OK for that cam. You can expect lower vacuum with a higher performance cam.
You probably find that the mix screw doesn't do much to alter the rpms.

yup had to confirm that, it's not really faster idle but it's more of a smother idle. and the vacum is actually very good for that cam, I have a 264/74 cam and I'm getting max 15 vac, also all over the place.

I have a manual, and i've found that I get better (stronger) idle at 10* timing, my cam is advanced 4*, have you tried to get the highest vacum in gear?

I recently was playing with the idle, It was at like 1200 also but the A/C kicked it to 850, I couldn't think why, till I saw it. because I modified my gas linkage, my old kick down was hitting the firewall not letting it idle any lower, well long story short it no longer hits, found better timing at 10* compared to 14* and was able to adjust to hit 900rpm, and AC kicks it to 650-700. not only that but I also no longer hit a ping under hard acceleration. the whole engine seems happier too.

I guess the point is try lower timing, and adjust air ratio for the smothest you can get, aka stop suttering, then go back to idle screw, also make sure you time without your vacum line hooked up to the dizzy. if adding the line adds vacum/advance it's fine, due to the fact the dizzy is meant for a stock vacum pull, hence the advance.

Richard

 

[mugsy]

I would've started with the cam timing straight up.

Normally I'd done that, but I was going with a tri-power set up right after a rebuild and was thinking of trying to push the power band a high as I could. Well I installed the cam at 4* retard and the engine barely would idle and it ran very hot. So I advanced it to 2* retard and again it would barely idle and the temps came down just a little. So if a little is "good" then more is "better" RIGHT! Realizing that the intake closing point is critical to idle quality I was going to advance the timing some more. So I took the freakin' front cover off AGAIN, and as I stood there looking at it, I said, "what the hey!" and advanced it to 4* advance. The idle quality, while better, is not close to what it was with the stock cam and missing the top piston ring on cylinder #6. At least the thing doesn't run so hot now. I still have a front cover gasket set and will do the cam re-timing one more time....

I've been taught to advance the static timing to get the most power out of it. It's either at 12* or 14* right now without any pinging . So knocking the timing back is counter intuitive to me, but I'll try that here shortly. Currently I'm in the middle of moving from Detroit to Pittsburgh.

And I've always timed the dizzy without the vac advance hose connected. Leaned that the hard way back in '78 .